Gold plating processes have many important industrial applications including the production of jewelry, optical devices, as well as the fabrication of electronic circuits and components.
In recent years, the use of gold in such industrial applications has been increasing very rapidly. At the same time, the cost of gold has been rising dramatically. For these reasons, it is economically advantageous to devise ways of saving gold, as well as ways of making gold plating processes more efficient. In particular, it is highly advantageous to be able to measure and control gold concentration in a convenient way.
There are several advantages to the use of gold as a surface metallic film. First of all, it does not form a surface insulating film such as an oxide film. This insures that gold has and retains a high surface luster which is quite attractive when used in jewelry articles. For the same reason, the optical reflectivity properties of gold are quite attractive which makes its use in optical devices highly desirable. Again, because no surface insulating film is formed, the use of gold in electric circuits and components is highly desirable. In particular, its use in electrical contact devices such as relays, contacts and electrical connectors is highly advantageous because surface contact to gold has low electrical resistance.
Gold also has the advantage of being chemically inert. This chemical property is responsible for the fact that no insulating or oxide layer is formed on the gold surfaces. Because of this chemical property, the use of gold insures long device lifetime and high device reliability since gold is not affected by most chemicals or adverse conditions of temperature and humidity. This is particularly advantageous in the production of integrated circuits where relatively thin conducting paths are often used. Here, stability and chemical inertness are unusually important so that the properties of these conducting paths are not changed with time. Many metals (for example, copper) might have satisfactory electrical properties for these applications, but they rapidly degrade with time, and alter their conductive properties. In addition to the inert chemical properties of gold, it also has the advantage of exhibiting high electrical conductivity.
Because of its high electrical conductivity, and chemical inertness, gold is often used as an electrical contact metal in electrical connectors, switches and relays. By the addition of small amounts of various elements (for example, arsenic, cobalt, nickel, etc.), gold can be made quite hard and resistant to abrasion. Thus, gold makes an excellent electrical contact metal for connectors and relays and is extensively used in this application.
It is highly advantageous economically to be able to produce reliable electrical contacts very rapidly and at low cost. In particular, rapid gold plating procedures are highly desirable. In order to insure gold plating quality, it is desirable to be able to monitor gold plating efficiency. This requires a method of measuring gold concentration very rapidly and in such a way that the results are immediately available. Most procedures for determining gold concentration either are very slow and yield results only after extensive chemical manipulations, or are unduly sensitive to the type and concentration of the supporting electrolyte used in the plating bath, or depend on the chemical state of the gold. In some gold plating procedures, it is advantageous to have a continuous monitoring procedure which indicates gold concentration in the plating bath.